HOLLANDAISE SAUCE A rich, lemon-flavored butter sauce thickened with egg yolks. The French chef who created this sauce named it for Holland probably because Holland was famous for its butter, a main ingredient in the sauce. Hollandaise sauce is often served over asparagus or poached salmon. Many sauces are based on Hollandaise such as Bearnaise and Mousseline. Because Hollandaise can curdle if even slightly overcooked, it needs close attention, low heat and constant stirring.